-XImpredicativeTypes implies -XRankNTypes, and improve error msg in TcMType

[ghc-hetmet.git] / compiler / typecheck / TcMType.lhs

diff --git a/compiler/typecheck/TcMType.lhs b/compiler/typecheck/TcMType.lhs
index 6de3dd2..75ce6c9 100644 (file)
--- a/compiler/typecheck/TcMType.lhs
+++ b/compiler/typecheck/TcMType.lhs
@@ -1066,6 +1066,7 @@ checkValidMonoType ty = check_mono_type MustBeMonoType ty
 data Rank = ArbitraryRank        -- Any rank ok
           | MustBeMonoType       -- Monotype regardless of flags
          | TyConArgMonoType      -- Monotype but could be poly if -XImpredicativeTypes
+         | SynArgMonoType        -- Monotype but could be poly if -XLiberalTypeSynonyms
           | Rank Int             -- Rank n, but could be more with -XRankNTypes
 
 decRank :: Rank -> Rank                  -- Function arguments
@@ -1139,7 +1140,7 @@ check_type rank ubx_tup ty@(TyConApp tc tys)
        ; liberal <- doptM Opt_LiberalTypeSynonyms
        ; if not liberal || isOpenSynTyCon tc then
                -- For H98 and synonym families, do check the type args
-               mapM_ (check_mono_type TyConArgMonoType) tys
+               mapM_ (check_mono_type SynArgMonoType) tys
 
          else  -- In the liberal case (only for closed syns), expand then check
          case tcView ty of   
@@ -1216,6 +1217,7 @@ forAllTyErr rank ty
     suggestion = case rank of
                   Rank _ -> ptext (sLit "Perhaps you intended to use -XRankNTypes or -XRank2Types")
                   TyConArgMonoType -> ptext (sLit "Perhaps you intended to use -XImpredicativeTypes")
+                  SynArgMonoType -> ptext (sLit "Perhaps you intended to use -XLiberalTypeSynonyms")
                   _ -> empty      -- Polytype is always illegal
 
 unliftedArgErr, ubxArgTyErr :: Type -> SDoc